In modern surgery, one of the most important instruments available to medical personnel is the powered surgical tool. Typically, this tool includes a handpiece in which a motor is housed. Secured to the handpiece is a cutting accessory. The cutting accessory is designed for application to a surgical site on a patient to accomplish a specific medical task. Some powered surgical tools are provided with drills or burs for cutting bores into hard tissue or for selectively removing the hard and soft tissue. Still other powered surgical tools are provided with saw blades as cutting accessories. These tools are used for separating large sections of hard and/or soft tissue. The ability to use powered surgical tools on a patient has lessened the physical strain of physicians and other medical personnel when performing procedures on a patient. Moreover, most surgical procedures can be performed more quickly, and more accurately, with powered surgical tools than with the manual equivalents that preceded them.
U.S. Pat. No. 5,888,200, entitled, MULTI-PURPOSE SURGICAL TOOL SYSTEM, issued 30 Mar. 1999, incorporated herein by reference, discloses a surgical tool system designed for a number of different applications. This tool system includes a handpiece in which a motor is housed. The handpiece also includes a first coupling assembly for selectively coupling the shaft of an accessory to the motor shaft. This handpiece also includes a second coupling assembly. The second coupling assembly is used to selectively secure an attachment to the front end of the handpiece. This attachment may include its own drive shaft and accessory coupling assembly. These attachments are elongated attachments, angled attachments and/or able to actuate saw blades. Thus, an advantage of providing this type of tool system is that a single handpiece can be used to drive a large number of different cutting accessories and facilitate the positioning of the accessories at the surgical site in a manner that is either required or desired for a particular surgical procedure.
A variation on this tool system is disclosed in U.S. Pat. No. 6,562,055, entitled CUTTING ATTACHMENT FOR A SURGICAL HANDPIECE DESIGNED TO BE SELECTIVELY COUPLED TO THE HANDPIECE, issued 13 May 2003 the contents of which is also explicitly incorporated herein by reference. This document discloses a surgical tool with a drive shaft that has an elongated bore. The drive shaft bore is sized to receive the proximal end of the shaft of the accessory. A collet is mounted to the drive shaft to rotate with the drive shaft. The collet has feet that project into the drive shaft bore. This assembly is further designed so that the accessory shaft can be selectively longitudinally positioned relative to the collet feet. This accessory is formed to have plural retention features disposed longitudinally along the length of the drive shaft. These features allows the practitioner to selectively set the extent to which the accessory shaft extends forward of the handpiece. Specifically, the practitioner may want to set the distal end of the accessory shaft, the end to which the tissue working member is attached, to extend a relatively short distance forward of the handpiece the shaft. The accessory is so set by positioning the accessory shaft so the distally located retention features are engaged by the collet feet. Alternatively, the practitioner can reposition the cutting accessory so that the tissue working member is located a relatively long distance away from the handpiece. To so configure the system, the shaft if longitudinally set relative to the collet so the proximally located retention features are the retention features against which the collet feet engage.
An advantage of the above construction is that a single cutting accessory can be positioned so that accessory head is located different distances from the handpiece. This eliminates the need to provide plural cutting accessories constructed so that the only distance between two different accessories is the overall length of the accessory shaft.
The above type of surgical tool system works well when the accessories have rigid shafts.
However, a number of different surgical tools system are provided with cutting accessories that have shafts that relatively thin and/or flexible. One type of surgical tool system provided with this type of thin flexible cutting accessory shaft is a minimally invasive surgical (MIS) tool system. An MIS tool system, as implied by its name, is designed to be applied to the surgical site in the patient through a relatively small opening, called a portal, formed in the patient. An objective behind performing an MIS procedure is to minimize the size of the incision that is formed in the patient to access the site internal to the patient at which the procedure is to be performed. One reason this objective is desirable because it reduces the extent to which the patient's tissue needs to be returned to its original state and heal after surgery. Another advantage of performing an MIS procedure, as opposed to a procedure in which a larger incision is formed, is that the MIS procedure lessens the extent the tissue and organs internal to the body are exposed to the ambient environment. By extension, this reduces the extent to which the tissue of the patient is open to infection.
Many tools designed to perform an MIS procedure are relatively small in cross sectional width. This facilitates the fitting of the tool in the relatively small diameter portal formed in the patient. Some MIS tools are designed to be inserted into a circular opening that has a diameter of 2 cm or less. These tools themselves may have cross section diameter of 0.5 cm or less.
There are powered surgical tools, including cutting accessories, designed to be seated in these small diameter bores. Often this type of tool system has a front end attachment designed to be releasably attached to the handpiece. The cutting accessory is rotated by the handpiece motor and rotates within the attachment. Some of these attachments have longitudinal axes formed with a bend. The accessory shaft is flexible so the shaft bends the accessory is bent or angled.
For the accessory shaft to bend or flex or to fit within a small diameter attachment, the accessory shaft is typically designed to be relatively small in diameter. The flexible section of some accessory shafts have a diameter of 2 mm or less.
Problems arise owing to the small size and flexibility of these accessory shafts. These shafts can flex or rotate when inserted in handpiece. This flexure is generally away from the longitudinal axis through the shaft. The rotation is generally around the longitudinal axis. The flexure can occur during the process of inserting the accessory in the handpiece. When the flexure occurs, it may be necessary to rotate the shaft to place the shaft in a position in which the retention features are aligned with the complementary retention features integral with the chuck. Having to take this action can contribute to the overall time it takes to perform a surgical procedure. Adding the time to perform this task to the procedure goes against one of the objective of modern surgery. Specifically, it is goal of modern surgery to perform the procedure as quickly as possible to minimize the time the patient is held under anesthesia and the body of the patient is open and exposed to the ambient environment.
The undesirable rotation of the accessory shaft can occur during the procedure when the handpiece is actuated. Specifically, when the handpiece is rotated, the whole of the accessory shaft is supposed to rotate at the same speed. However, owing to imposition of different forces on the different portions of the accessory and the flexible nature of the accessory shaft, there may some twist in the accessory shaft around the longitudinal axis of the shaft. As a result of this twist, and the natural tendency of the material forming the shaft to twist back to the untwisted state, the proximal end of the accessory shaft, the end of the shaft disposed in the drive shaft integral with the handpiece may want to rotate within the drive shaft. This rotation of the shaft can result in the shaft retention features rotating out of engagement with the collet feet or other chuck retention features that hold the shaft in position. If this type of accessory shaft-relative to-drive shaft movement occurs, the accessory shaft may not be firmly held in place to the drive shaft.